This invention relates to a gas shielded arc welding method suitable for application to the welding of aluminum or aluminum alloys, magnesium or magnesium alloys, as well as titanium or titanium alloys, in particular to the welding of titanium and titanium alloys.
Active metals such as titanium and titanium alloys have high affinity for oxygen and nitrogen, so if air entrapment occurs during welding, they absorb the oxygen and nitrogen in the air and the weld is contaminated to have a brittle structure. Therefore, titanium and titanium alloys are commonly welded by gas shielded arc welding with a shielding gas being blown through a nozzle against the area being welded.
One applicable method of gas shielded arc welding is the MIG (metal inert gas) process in which a welding wire as a consumable electrode also working as a filler metal is passed through a hole in a contact tip fitted within the gas nozzle and an electric current is applied to the wire as it is melted to permit welding. The conventional MIG process, however, suffers from the disadvantage of being unable to achieve satisfactory welding in titanium and titanium alloys.
The gas nozzle used in the conventional MIG process is a pipe having a uniform inside diameter throughout from the orifices to the distal gas outlet. The shielding gas, particularly the circumference of its flux, that has been ejected from the nozzle (the gas is usually argon or helium having a smaller specific gravity than CO2) deviates outward halfway its travel toward the area to be welded; as a result, the area to be welded is insufficiently shielded from the surrounding air that the atmospheric oxygen and nitrogen are entrapped in the weld to produce a defective structure and this is probably the reason for the above-mentioned poor performance of the conventional MIG process.
The gas shielded arc welding method of the invention has been developed in order to solve the aforementioned problem of the conventional MIG process.
The first embodiment of the method is for performing arc welding with a shielding gas being ejected from a nozzle, characterized in that the nozzle comprises a straight portion that permits the shielding gas flows from orifices to flow parallel to the axial direction and a constricted portion continuous from the straight portion that constricts the gas flows from the straight portion as they travel toward the distal end, the nozzle satisfying the following relations (1) and (2):
xe2x80x831.5xe2x89xa6(Dp/Do)xe2x89xa62.5xe2x80x83xe2x80x83(1)
1.0xe2x89xa6(L/Dp)xe2x80x83xe2x80x83(2)
where Dp is the inside diameter of the straight portion, Do is the inside diameter of the distal gas outlet of the constricted portion, and L is the axial length of the constricted portion.
As the second embodiment of the invention, the method above may be controlled so that the nozzle further satisfies the following relation (3):
1.3xe2x89xa6(Ls/Dp)xe2x80x83xe2x80x83(3)
where Ls is the axial length of the straight portion.
As the third embodiment of the invention, the methods above are to weld any one active metal selected from among titanium, titanium alloys, aluminum, aluminum alloys, magnesium and magnesium alloys.